1. Field of the Invention
The present invention relates to a sensor for detecting a foreign body, and particularly to a linear sensor for detecting a foreign body pinched between a vehicle body and an opening and closing body such as a door in a vehicle such as an automobile.
2. Related Art
Conventionally, some vehicles such as the so-called minivan include a slide door for sliding along a body of the vehicle so as not to separate the door from the body while improving convenience of getting on and off the vehicle by widely opening and closing a platform of occupants. Also in recent years, devices for automatically opening and closing this slide door using a motor etc. are known.
In a system for opening and closing such a door, it is necessary to be constructed so as not to pinch foreign bodies (for example, the human body or clothes) during automatic closing of the slide door. Because of that, a sensor for detecting the foreign body and a mechanism for performing reverse control in an opening direction while stopping the slide door when the foreign body is, detected by the sensor are provided. Here, as the sensor, a capacitance type sensor made by arranging two opposed electrodes inside a linear cover body is proposed.
The capacitance type sensor is a sensor for detecting the foreign body based on a change in capacitance measured through the electrodes, and can detect the foreign body having relatively large capacitance such as the human body in a noncontact state. Also, a technique for disposing space between both electrodes in order to improve accuracy of detection with respect to the foreign body having relatively small capacitance is proposed (for example, see JP-A-2000-329506). According to the technique, a distance between both electrodes can be changed greatly even when a pressure at the time of making contact with the foreign body is relatively low. As a result, the amount of change in capacitance can be increased and the foreign body can be detected with high accuracy.
However, according to the art described above, at least two electrodes are required. Also, the respective electrodes must be placed in predetermined positions of the inside of the linear cover body while maintaining a positional relation between the two electrodes. Because of that, it becomes difficult to manufacture the sensor. That is, the art described above is not necessarily advantageous in aspects of manufacturing work and the number of components and as a result, a manufacturing cost may increase.